Lice are a common pest which are widely distributed throughout the world and infest both humans and animals. They are spread by contact and are a problem even under relatively sanitary conditions.
Lice are insects about two to three millimeters in length. They lay eggs called nits, which look like white grains of sand and are firmly attached to the hairs by a cementlike excretion. The eggs generally hatch in about eight to ten days at body temperature.
The common latin name for the whole family is "Anoplura". Human lice are divided into two genera: Head lice, Pediculus capitis or Pediculus humanus capitis, and Body lice or Clothing lice, Pediculus humanus humanus or Pediculus corporis; and Pubic lice, Phthirius pubis. Lice are spread by crowding and common usage of clothing and combs. Initially, infestations result at most in irritation, which can lead to infection of the irritated area, although there are at least three major diseases that are primarily transmitted by lice: epidemic typhus, trench fever and relapsing fever.
Lice on animals such as the dog are commonly associated with itching and are found under matted fur and around the ears, head, neck and shoulders. There are two types of lice, biting lice that feed on skin scales and sucking lice that feed on the dog's blood and can cause a severe anemia.
Special combs are used to remove the eggs from the hair. Lice are usually treated by application of an insecticidal product, such as 0.1 to 2% pyrethroids with synergists, 68% benzyl benzoate, 6% DDT, 12% benzolaine and 14% Tween.TM. 80, diluted 1:5. Several insecticides have also been used for treatment of body lice, including 10% DDT, 1% lindane, and pyrethrum powders. Animals are treated with the insecticide three to four times at ten day intervals, along with cleaning or disposal of associated bedding. It would clearly be preferable to have a treatment which prevents infestation, rather than a treatment after infestation of either a person or an animal. Although a number of insect repellents have been developed, most are relatively specific to a particular type of insect, such as mosquitos, or smell bad, which would limit usefulness under routine conditions, as in a school for young children. Compounds that have been used for control of insects such as mosquitos include DEET (diethyl toluamide) and some terpenoids, as reported by Hwang, et al, J. Chem. Ecol., 11, 1297 (1985); and Ruledge, J. Am. Mosquito Control Assoc. 4, 414 (1988). In the work reported by Hwang, et al., a screen done on terpenoids as mosquito repellent indicated that terpenoids are effective repellents. Ruledge notes that .alpha.-terpineol is useful in mosquito repellent. U.S. Pat. Re. No. 29,829 to Bordenca, et al., discloses that lower hydroxyalkyl amines in which at least one of the amino hydrogens is replaced by an acyclic monoterpenyl radical or hydrogenated acyclic monoterpenyl radical are useful insect repellents. U.S. Pat. No. 4,193,986 to Cox, U.S. Pat. No. 4,759,930 to Granirer, et al., U.S. Pat. No. 4,671,960 to Thielen, et al., and U.S. Pat. No. 4,587,123 to Price claim that eucalyptus oil is an effective flea repellant.
None of these repellents is specific for lice nor proven to be efficacious.
It is therefore an object of the present invention to provide repellents for lice that are safe, efficacious, pleasant smelling, and relatively inexpensive, but which do not contain toxic insecticides.
It is another object of the present invention to provide such repellents that are effective in a variety of carriers, including hair sprays, shampoos, and powders.
It is still another object of the present invention to provide such repellents that are effective in repelling both human and animal lice.